1. Field of the Invention
The invention relates generally to the formation of diamond coatings and their application to drilling bits and other drilling tools. In particular aspects, the invention relates to techniques for preparing and applying such coatings using a tape casting procedure.
2. Description of the Related Art
Drilling tools, including bits, are typically formed of a steel core that is enclosed in a tungsten carbide shell. Hardfacing may be applied to portions of the outer surface of the bit or tool. Polycrystalline diamond (PCD) is used to protect those portions of a drill bit or other drilling tools that are subjected to the most extreme wear forces during drilling. Conventionally, PCD inserts are incorporated into the surface of the tool. Alternatively, diamond grit may be incorporated into the surface. In these instances, the diamond coatings or inserts are often prone to removal from the substrate during use within the borehole. A further problem associated with these techniques is the distribution of the diamond particles. Too few diamond particles concentrated in one area will lead to points of weakness and wear during intensive and sustained use within a borehole.
Traditionally, when small superhard particles are used to coat a substrate, they are first mixed into with a metal bonding matrix that might consist of cobalt powder or powder of another metal. This mixture is then sintered to consolidate it, and the consolidated mixture is applied to the substrate. This technique has a number of problems. First, the consolidated mixture must be maintained at a relatively high temperature during application to the substrate. This requirement adds a level of difficulty in handling during application to the substrate. Additionally, the viscous and non-uniform nature of the metal bonding matrix makes it difficult to achieve a uniform distribution of the superhard particles within the consolidated mixture.
U.S. patent application Publication No. 2002/0077054 A1 by Sung describes a method of applying a diamond coating to tools, such as diamond saws and the like. In the described method, diamond particles are disposed into a sheet of matrix support material. To accomplish this, a sheet of matrix support material is first formed from conventional powders, such as cobalt, nickel, iron, copper, bronze, or other suitable bonding agents. To form the sheet, a matrix powder is mixed with a binder to form a slurry. The slurry is poured onto a plastic tape and pulled underneath a blade or leveling device. The slurry is then cast into a plate with a desired thickness by adjusting the gap between the tape. Thus, while a tape casting method is employed, it is only utilized to create a thin film of binder material. Following this casting and formation process superhard inserts, or particles, are placed into the binder tape by disposing a template with many apertures over the already-cast tape of binder. The superhard particles are then spread over the template and into many of the apertures. Those particles that do not enter one of the apertures are then swept off of the template with a broom or the like. Those particles that are not swept away from the template are then pressed into the binder tape using a flat steel seating plate to seat the particles.
There are a number of weaknesses and drawbacks to Sung's method. First, even if done very carefully, the step of brushing unseated particles away from the template may move, or actually remove, some of the particles that are seated within apertures in the template. Additionally, some of the superhard particles may adhere to the template or to the seating plate rather than being pressed into the binder tape. As a result of these problems, there will inherently be gaps and weaknesses in the resulting coating.
Tape casting is a process that has been used for the creation of generally thin films and sheets, including ceramic substrates for capacitors, sensors, catalysts, and heat exchangers. Examples of conventional tape casting methods are found in Andreas Roosen, “Basic Requirements for Tape Casting of Ceramic Powders,” Ceramic Transactions, Volume 1, Part B, Ceramic Powder Science, The American Ceramic Society, Inc. (1988). Typically in tape casting, a very thin tape is created and then dried immediately to evaporate solvents within the tape. The resulting tape may then be cut, punched, or scored, as required by its end use. To the inventors' knowledge, tape casting has not heretofore been utilized for the creation of diamond-based coatings or films.
Additionally, there are methods known for creating ceramic tapes and applying printed circuitry, including capacitors, electrodes, and other conductive components, thereupon. Printed circuitry tapes of this type are used, for example, in creating an oxygen sensor for use in the automotive industry, and other relatively light duty applications. A method for creating such a sensor is described in European Patent No. EP 0 134 709 B1 entitled “An Oxygen Sensor Element.” Printed circuitry tapes are generally considered unsuitable for use upon the surfaces of downhole tools, such as drill bits and bottom hole assemblies, since there are not effective means for protecting the circuitry from being scraped off or being otherwise damaged by physical wellbore hazards or being quickly degraded by high temperatures and chemical hazards. A further obstacle to the potential use of printed circuitry tapes with downhole tools is the lack of adequate heat sinks that can be readily incorporated into the structure.
An improved method of effectively forming and applying diamond-based coatings would be desirable. Additionally, improved methods and systems for incorporating diamond-based coatings into coatings having layers of preprinted circuitry therein would be desirable.